ADF - Customize a <af:commandButton> width the property styleClass

Question

I all, I'm new to the ADF language and after a long search and failed tries, I have to ask how can I change a button layout - background, border, ... - using the CSS and the property "styleClass" of the ADF?

In my .jspx I have something like:

<af:commandButton action="#{backing_test.echoAction}" id="echo1"  text="Save 1" styleClass="commandButton.buttonSaveTest" />

The thing is, after opening firebug, I found out that instead of a regular button, I have an image!

Thanks for you help!